1. Field of the Invention
This invention relates generally to an apparatus for reproducing information recorded on optical record discs, such as digital audio discs or video discs, and more particularly, to drive control circuits for pick-up devices of a disc information reproducing apparatus.
2. Description of Related Art
There have been provided optical record discs which store optically recorded information data or signals such as digitized audio signals, video or image signals and record disc reproducing apparatus for reproducing the recorded information data. Such the optical record discs for example compact discs (CD) (a type of digital audio discs), optical video disc, optical discs and the like are so arranged that digital data intended for high density recording are recorded in the form of pit strings forming a spiral track or a plurality of concentric tracks on one side of the disc and reproduced through reading the pit strings by means of a transducer means such as an optical pick-up device using laser beams. The optical pick-up device is provided with a lens for placing the laser beam on the record disc and a lens actuator for controlling the laser beam placing lens, etc., and a carriage thereof so that the pick-up device may accurately follow or trace the continuous concentric tracks or the spiral track. The range that the beam placing lens may move in the pick-up device is limited to, e.g., the range corresponding to dozens of tracks or so. Additionally, there is further provided a pick-up actuator for moving the pick-up device radially with respect to the disc surface, in the disc information reproducing apparatus.
Therefore, the disc information reproducing apparatus is so provided that the pick-up device may track the continuous concentric tracks or the spiral track through a cooperation of the lens actuator for controlling the beam placing lens and the pick-up actuator for controlling the pick-up device. Drive signals for the lens actuator and the pick-up actuator are usually obtained from a tracking error signal obtained in response to deviation of the laser beam from the center of the track. A lens actuator drive signal works for making the beam placing lens deviate from its standard position in the pick-up device, while a pick-up drive signal works for moving the pick-up device so that the deviation of the beam placing lens from the standard position decreases. The lens actuator may move the beam placing lens in response to the lens actuator drive signal with a relatively high sensitivity because the beam placing lens has a relatively light mass, while the pick-up actuator may move the beam placing lens in response to the lens actuator drive signal with a relatively low sensitivity because the pick-up device has a relatively heavy mass. Moreover, there are a large friction and a backlash in a mechanical coupling between the pick-up device and the pick-up actuator. Therefore, in the reproducing operation for continuously tracing the concentric tracks or the spiral track radially in reference to the record disc, the pick-up device moves intermittently after the beam placing lens is deviated from the standard position in each direction in respect to the record disc for about 200 micrometers (.mu.) corresponding to a a range of about 120 number of tracks.
Further, in conventional disc information reproducing apparatus, the pick-up drive signal or voltage is continually applied to the pick-up actuator, while the pick-up device is left unmoved until the pick-up drive voltage has increased to a level sufficient to drive the pick-up device against the mass, the friction and the backlash. In other words, the pick-up device is moved intermittently in spite of the pick-up drive voltage being always applied thereto. This causes power responding to the pick-up drive voltage to be consumed wastefully during the period that the pick-up device is left unmoved. The power consumption has become a serious problem for battery-driven record disc repoducing apparatus type. Further, there has occured an undesired mechanical vibration or a noise at the mechanical coupling between the pick-up device and the pick-up actuator during the period that the pick-up device is left unmoved.